Automotive battery-powered applications preferably include reverse-voltage protection to prevent damage to the downstream circuitry (e.g. power supplies) by high voltage surges, reverse battery and cold crank faults. Also many mobile devices derive their power or recharge their internal batteries from multiple alternative inputs such as AC wall adaptors and USB ports. A user may unknowingly plug in a wrong adaptor, thereby damaging the device with a high or even a negative power supply voltage.
A blocking diode in series with the power supply has been used to address this problem, but such a solution causes extra power loss, generates heat and reduces the available supply voltage range. In automotive applications, the extra voltage drop across the diode is particularly undesirable during cold crank. More power efficient solutions have been designed to replace the diode with a p-channel MOSFET or an n-channel MOSFET at expenses of a significant amount of external components, thus increasing costs and space of the board. The number of external components can be even higher to include reverse current protection in cold crank faults.
By way of example, Linear Technology Corporation of Milpitas Calif. has a product number LTC4365 which provides undervoltage, overvoltage and reverse-supply protection. The LTC4365 includes a pair of back-to-back MOSFETs controlled by a common GATE signal to open or close a connection between VIN (e.g. a battery voltage supply) and VOUT (e.g. to downstream circuitry such as a powers supply).
While the LTC4365 does provide undervoltage, overvoltage and reverse supply protection, it does not provide for the protection of the oxide of the external MOSFETs with, for example, a zener diode because the MOSFETs would be turned on during reverse battery faults, thereby potentially damaging the downstream circuitry. Instead, the LTC4365 limits the input voltage and uses an expensive TVS load dump protection. Furthermore, the LTC4365 requires a high speed comparator to follow fast negative transients.
These and other limitations of the prior art will become apparent to those of skill in the art upon a reading of the following descriptions and a study of the several figures of the drawing.